On the subject of Kamui...I kinda doubt we'll see him/her. I can't see Sakurai prioritizing another Fire Emblem character as DLC when we already have Roy coming up, and by the time Smash 5 rolls out, Fire Emblem If will be old news. It'll be in the same "not represented with a playable character" bin with FE2, 4, 5, 7, and 8.
One serious thing to consider is that Fire Emblem characters, if you're not a Marth Clone, retained from being major in multiple titles.
has his two games and their remakes,
was the protagonist of only 9 when he got in but 10 was plotted by the development time of Brawl considering how clear 9 was going to get a sequel by the ending.... and while
is only in Awakening, the "MyUnit" character which Robin effectively is was first used in a more limited scope in FE12... like someone's fan fiction. Kamui obviously being the third sequential usage of the My Unit character but with Dracostones instead of tomes.
With how balls-out 14 is being with the three stories that are going to make up it after the DLC, I highly doubt it would get a continuation at all, let alone before Smash 5.